#  条件判断：if-elif-else,从上往下判断
# eg1
age = 20
if  age >= 6:#注意加冒号
    print('teenager')
elif age >= 18:
    print('adult') 
else:
    print('kid')
    
# eg2 CalBMI
height,weight = eval(input('请输入身高(米)和体重(公斤）[逗号隔开]:'))
bmi = weight / pow(height,2)
print('BMI数值为：{:.2}'.format(bmi))
who,dom = "",""
if bmi < 18.5:
    who,dom = "偏瘦","偏瘦"
elif 18.5 <= bmi < 24:
    who,dom = "正常","正常"
elif 24 <=  bmi < 25:
    who,dom = "正常","偏胖"
else:
    who,dom ="肥胖","肥胖"
print("BMI指数为：国际{},国内{}".format(who,dom))

#input()返回字符串
present = ("请输入一个自然数：")
print(present)
